Automatically and selectively adjustable variable displacement pump



NOV. 22, 1955 B R ET AL 2,724,339

AUTOMATICALLY AND SELECTIVELY ADJUSTABLE VARIABLE DISPLACEMENT PUMP Filed June 25, 1949 2 Sheets-Sheet 1 /& H11 5 fication of its pressure responsiveness.

United States PatentOfifice 2,724,339 Patented Nov. 22, 1955 AUTOMATICALLY AN D SELECTIVELY ADJUST- ABLE VARIABLE DISPLACEMENT PUMP Bernard E. OConnor, Buffalo, and Alfred G. French, East Aurora, N. Y., assignors to Houdaille-Hershey Corporation, Detroit, Mich., a corporation of Michigan Application June 25, 1949, SerialNo. 161,334 9 Claims. (c1. 103----120) for automatically and selectively adjusting the displacement of such pumps. 7

Another object of the invention is to provide improved displacement control means for variable displacement pumps responsive to pump created pressure and also operable for selectively varying the pump pressure I responsiveness.

A further object of the invention is to provide novel pressure responsive control valve means for adjusting the displacement of the variable displacement pump and which control valve means is adapted for selective modijStill another object of the invention is to improve the general construction of variable displacement pumps. Other objects, features and advantages of the present invention will be readily apparent fromthe following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings in which:

Figure l is a more or less schematic elevational view of a variable displacement pump embodying the features of the invention and having the face plate thereof removed to reveal internal structure of the pump; Figure 2 is a composite transverse, sectional view through the pump taken substantially on the line IIII of Figure 1 and showing the face plate assembled in Figure 3 is a fragmentary sectional detail view taken substantially on the line III-III of Figure 1;

Figure 4 is a vertical sectional view taken substantially on the line IV-IV of Figure 2; and

Figure 5 is a fragmentary sectional detail view taken substantially on the line V-V of Figure 4. p H .In the present instance a variable displacement pump of the sliding vane type has been illustrated comprising a unit including, a casing 10 providing a housing for a pump rotor 11 which has a uniformly spaced series of radial peripheral slots 12 within which sliding reciprocable vanes 13 are operably disposed. The sides of the rotor 11 are inset at a predetermined distance from its periphery at both sides to accommodate concentric rings 14 which engage the inner ends of the vanes 13 and function to maintain the outer ends of the vanes or blades on a predetermined diameter. An inner peripheral bore may be provided in the rotor 11 defined by spline teeth 15 by which the rotor is adapted to be assembled for rotation about a splined shaft such as a transmission shaft in an automotive vehicle or the like, where the pump unit is used in such an association.

A circular pump chamber 17 concentric with the control rings 14 and of a diameter to be constantly engaged by the outer tips of the vanes 13 is provided by a displacement control member or modulator 18. In the present instance the modulator 18 is of the reciprocably guided type having opposite parallel flat sides 19 slidably engaging parallel bearing walls 20 within a modulator control chamber 21 provided in a housing ring 22. In a desirable construction, the housing ring 22, the modulator 18 and the rotor 11 are approximately of the same thickness, that is, their faces are disposed in approximately the same plane with opposite facing plates or blocks 23 and 24 completing the housing or casing enclosing the pump and more particularly enclosing sides for the pump chamber 17 and the modulator chamber 21. In assembly, suflicient minute clearance is afforded after the facing members 23 and 24 have been secured to the opposite faces of the modulator casing member 22, as best seen in Figure 2, to permit free rotation of the rotor 11 and slidable reciprocation of the modulator ring 18.

In the operation of the pump, rotation of the rotor 11 is intended to be clockwise, as indicated by the directional arrow in Figure 1. Thereby hydraulic fluid from any appropriate source is drawn through an armateinlet duct 25 by action of the rotor blades 13 at the low pressure side of the pump and displaced through an outlet or discharge port 27 at the high pressure side of the pump. For this purpose the modulator member 18 is normally biased into eccentric pumping relation to the rotor 11 by means such as a biasing spring 28 working between the appropriate end of the modulator 18 and the modulator chamber housing 22, as best seen in Figuresl and 2. The spring 28 seats against a flattened end surface 29 on the modulator and within a socket 30 in the casing ring 22.

The principal function of the biasing spring 28, which may be of relatively light Weight and which need not be of any critical load or compression strength, is to as sure that the modulator 18 will normally be in a position of pump chamber eccentricity with respect to the rotor 11, and more especially during non-operating periods or intervals so that at least at the start of operation the modulator 18 will be in the position of maximum pump chamber eccentricity.

Means are provided for automatically adjusting the modulator 18 to vary displacement of the pump during operation in order to accommodate variable fluid demand conditions in the fluid system in which the pump is used; Such means comprise a control system utilizing pump pressure for automatically adjusting the modulatorin response to fluctuating demand. To this end, the construction and relationship of the modulator 18 and more particularly the opposite ends thereof and the walls of the modulator chamber 21 opposing the ends of the modulator is such that a fluid pressure sub-chamber 31 is provided at the spring urged end of the modulator and a fluid pressure sub-chamber 32 is provided at the opposite end of the modulator and a system of pressure ducts alternatively communicable with the high pressure and low pressure sides of the pump communicate with the pressure chambers 31 and 32 Control of the fluid passages is effected by the valve assembly 33.

According to the present invention not only the fluid ports 25 and 27 but also the various modulator control passages are formed in the facing block or plate 24 and the valve assembly 33 is also operatively disposed in the facing plate 24., To this end, the arcuate ports 25 and 27 are formed in the inner face of the plate 24 so as to be in direct communication with the pump chamber 17 within the modulator. Communicating directly with the ends of the ports 25 and 27 at the maximum operating eccentricity side of the pump chamber 17 is a valve bore 34 having an intermediate smaller diameter portion 35 within which is slidably reciprocably bearinged a valve plugorbody 37. A plug 3'8 closes one end of the bore "has an axial bore Within which is fitted a'bushing ring 42 sealing and providing an inner wall for the duct or passage afforded by the groove 41. From the passage groove 41 leads a bore 43 (Figure 3) communicating with an intersecting bore 44 providing a port opening into the modulator control sub-chamber 31 (Figure 1).

The fluid passage bore 40 is'located adjacent to the end :of the highpressure port 27 while adjacent to the low pressure port 25 is provided a similar parallel fluid passage 'bore '45 also intersecting the valve bore and communicating with the passage groove 41. The bores 40 and 45 *may conveniently be drilled in from the edge of the facingplate .24 and are plugged at their outerends by means of suitable closure plugs 47.

Communication between the smaller diameter portion '35 ofthevalve chamber or bore and the modulator con- *trol sub-chamber 32 is effected. by means of preferably identicallow and high pressure passage bores 48 and 49 (Figures 2, 4 and located intermediate the bores 40 and '45 and'opening through the inner face of the facing plate '24 to communicate with respective passage bores 50 and 51 in'the modulator housing ring 22 and opening into -the modulator control sub-chamber 32.

' In order to assure that the chambers 31 and 32 will be at 'all'times open to the communicating ports of the control 'system, the respective ends of the modulator are appropriately formed with respect to the corresponding ends of the modulator chamber 21. To this end .the flattened modulator end'29 is formed narrower than an opposing flattened wall portion 52 defining the end wall of the chamber 21 and within which the'spring socket 30 is formed. The remaining portions .of the respective surfaces of the modulator end and the chamber wall defining the sub-chamber 31 are relatively formed, as for example,

cinrespectivearcs which assure that even when the modulater is moved in opposition to the biasing spring 28 until contact is .eflected'between the flattened end 29 and the stop end-52, a chamber gap will persist in communication-vvith theport bore 44.

"Similarly at the modulator control sub-chamber 32,

the end of the modulator 18 is formed with a flattened end including a stop portion 53 which engages aeornpleinentary flattened end portion 54 of the end wall of the modulator chamber in the fully eccentric condition of the modulator, while a stepped orotfset flattened portion 55 o'f the modulator end maintains .a space which afiords communication of the port'bore 50 with the sub-chamber 32 which may also be defined by spaced arcuate wall portions of the modulatoruand the modulator housing ring 22 persisting in substantial spaced relation in the fully eccentric position of the modulator. In this .fully eccentric position of the modulator, by preference the portboreI50is blocked in the fully eccentric condition of the modulator.

Thefunction of the valve :assembly'33 is to so control delivery of high pressure fluid to the opposite-ends of the modulator or suction of .fluid from such opposite ends of the modulator as to properly control the pump chamber eccentricity position of the modulator for given volume demands in the operation of the pump. To this end a pressure shoulder 57 on the valve member 37 is exposed to high pressure fluid from the high pressure p rt 27, such pressure working against a valve loading spring 58 acting between the closure plug 38 and the opposing end of the valve body and normally acting to urge the valve member toward the high pressure port 27 withapredeterminedforce.

At the start of the pumping action of the rotor 11 and the vanes 13, it is desirable that the modulator 18 be maintained in its maximum pump chamber eccentricity positioned so that pressure will build up rapidly in the pump. For this purpose means are provided for initially bypassing pressurefluid to the modulator subecharnberZ-31 to supplement the action of the initial .biasingspring 28. Such means comprise .a series of passages or orifices 5.9 through the pressure shoulder '57 of the valve member and communicating by way of an annular groove 60 .in the periphery of the valve member 37 with the communication passagebore 40. Therefore, until sufiicientpressure has been developed inthe pump to drive the valve member 37 in opposition to theload of the spring 58, pressure fluid will by-pass to the spring loaded end of the modulator 18 and thus act to hold the modulator effectively against pump displacement curtailing shifting. At the same time, the modulator control sub-chamber 32 'is placed "in fluid bleed ol-f communication with'theflow pressure side of the pump by way of the passageway including the orifice "bore '50, the passage bore .48, an annular peripheral groove 61 on the valve body .37 and a series of longitudinally extending orifices or small bores 62 in the rear portion of the valve body opening into the spring chamber behind the valve body within the'bore 34 and thus communicating with thelow pressure or suction port '25 of the pump.

When the pump pressure becomes great enough to act upon the pressure shoulder 57 of the valve body to overcome the load of the spring '58, the valve body .37 is shifted against the spring until the annular grooves 60 and '61 in the valve body are displaced from communication with the respectivepassage bores 40 and '50 and are fully blocked by portions of the wall of the reduced diameter bore section 35 interveningbetween the various fluid communication bores entering the valve bore. As this is accomplished a predetermined mean pressure factor is attained for the pump and the modulator 18 is held positively in a fluid lock against shifting-since the fluid which was conducted under pressure to the sub-chamber '31,.is trapped against substantial escape. Should the pressure of theypump tend to exceed the mean value desired .as established by the loading or rating of the spring '58 the pressure acting upon the pressure shoulder 57 further shifts the-valve member 37 until communication is established between the high pressure side of 'thepump through the peripheral groove '60 with the fluid passage 49and '51 to conduct *pressure fluid to the modulator control subchamber 32. At the same time the valve-groove 61 acts in coordination toeffect communication by way ,of the bore 45 between the low pressurezside of the pump and the modulator control sub-chamber 31 so that the piessure fluid working on the sub-chamber 32 end of the modulator acts to'drive the modulator toward reduced pump chamber eccentricity, whereby the pump displacement is modified and the pump pressure returns to the mean pressure value desired. Thereupon, the .spring' 58 again tends to return the valve member 37 in opposition to the pump pressure "until a valve-groove-blocking, .modulator-fluid-pressure-locking condition is again established, pending further fluctuations inpump pressure calling for modulation. Since, as'best seen in Figure 4, .the peripheral valve body grooves 60 and 61, are only a fraction as wide as the respective passage bores with which they are adapted to communicate in various positions of the valve body in operation, it will be observed :that only small movements of the valve body will be effective (to move the grooves .out of communication with the passage bores or orifices. Furthermore, since the ,imperforate or land areas between the respective passageway orifices are only. approximately aszwide as the valve-body grooves and in .any event only slightly wider in their spacing between passageway orifices, .-the sensitivity of :the :control valve member 37 for control purposes is substantially enhanced.

For certain purposes it becomes desirable to modify the pressure sensitivity or responsiveness of the valve member 37 during operation of the pump or. for. various phases of operation of the pump. According to the present invention this is accomplished by providing the valve body 37 ,Wlllh an integral reduced diameter piston head 63 extending coaxially from the pressure shoulder 57 and slidably bearing in a further reduced diameter extension 64 of the valve bore terminating in a blind end 65 beyond the communicating end of the high pressure port 27 of the pump. It will be observed, that the area of the attachment portion of the piston 63 reduces the total effective area of the pressure shoulder 57. Therefore, when the efiective area of the shoulder 57 is reduced by the effective area of the piston head 63, substantially greater pressure will have to be exerted against the shoulder 57 per unit exposed area to overcome the valve biasing spring 58 than where the entire effective area of the end of the valve member 37 including the shoulder 57 and the effective end area of the piston head 63 are exposed to valve pressure.

Means are provided for selectively varying the effective pressure area on the end of the valve member by either subjecting the effectivepressure end of the piston extension 63 to pump pressure or cutting off pump pressure from such valve head extension. To this end, a pressure passageway by way of a duct 67 communicating with the pressure port 27 and a. duct 68 communicating with the chamber provided by the reduced diameter bore portion 64 is provided and a valve 69 controls the flow of pressure fluid from the duct 67 to the duct 68. When not connected to the pressure duct 67, the duct 68 may be connected with atmosphere by Way of the valve 69 through a duct 70 or other passage or opening. When vented to atmosphere, the effective area of the valve head extension 63 is subtracted from the pressure area of the shoulder 57 and therefore greater pressure by a predetermined amount is required per unit area on the shoulder 57 to overcome the force of the biasing valve 58 and pumping pressure is correspondingly increased. On the other hand, when by operation of the valve 69, both the piston valve pressure area shoulder 57 and the pressure area of the end of the piston extension 63 are subjected to pump pressure, substantially lower unit pressure Will effect compression of the biasing spring 58 andtherefore a lower mean pumping pressure will be maintained in operation of the pump.

The tip of the piston extension 63 serves as a convenient stop for the forward end of the valve body by engaging against the blind end 65 of the reduced diameter bore portion 64. A further initial stage of pressure resistance can therefore be attained by having the piston head tip of substantial area which when abutting the blind end shoulder 65 will not be acted upon by pressure entering the piston chamber by way of theduct 68 and which pressure will initially act only upon a reduced area pressure shoulder 71 on the piston head. As a result, initially, pressure is effective only upon the pressure shoulder 57 and the limited piston pressure shoulder 71 and after the movement of the pistonbody 37 has been initiated then the additional pressure surface of the piston tip. becomes effective. This is a valuable feature at the beginning of operation when at least slight surging fluctuations in pressure are desirably resisted and a full pressure head will develop before the valve is shifted to provide a pressure lock or modulate the pressure.

From the foregoing it will be apparent that the present invention provides not only selective multi-stage pressure responsiveness in the pump but also inany such stage of pressure responsiveness automatic adjustment for variable displacement of the pump to maintain the mean pumping pressure desired for either of the selective stages or pressure ratings.

It will be understood that modifications and variations 6 may be effected without departing from the scope of the novel concepts of the present invention.

We claim as our invention:

1. In a constant pressure variable displacement pump, means defining a modulator chamber, a modulator movable therein and defining with the walls defining the chamber fluid sub-chambers separated by the modulator, the modulator having a circular pump chamber therein, a rotary impelleron a fixed axis operating in said pump chamber and having impelling means cooperating with the annular wall defining the pump chamber to vary the pump displacement as the modulator moves in said modulator chamber, said means providing a valve chamber, a reciprocal plunger valve in said valve chamber, a fluid pressure passage communicating with the head of the valve and with the high pressure side of the pump chamber and normally exposing the head of the valve to pressure created by the pump, a spring operating against the opposite end of said valve and normally biasing the valve to resist movement of the valve responsive to the pump pressure with predetermined force, a fluid passage communicating with the low pressure side of the pump, and respective fluid passages communicating with said subchambers, said plunger valve controlling said low pressure and said sub-chamber fluid passages and in its maximum spring biased position effecting communication between the low pressure fluid passage and the passage from one of said sub-chambers to assure displacement of the modulator into said one sub-chamber, the valve being movable by pump created pressure in excess of the spring bias directed thereto through said first mentioned passage to effect communication between the fluid passage from said one sub-chamber and the high pressure fluid passage from the pump and coincidentally effecting communication between the low pressure passage and the passage from the remaining sub-chamber whereby to cause shifting of the modulator toward or into said remaining subchamber, and means for modifying the sensitivity of the plunger valve to pump pressure including an integral piston extending therefrom, a passageway communicating with the high pressure side of said pump and with said piston, and a control valve in said passageway for selectively subjecting said piston extending from the valve plunger to high pressure from said passageway.

2. In a variable displacement pump, a casing defining a modulator chamber, a modulator movable in said chamber and providing a pump chamber, fluid pumping means operable in said pump chamber and adjustable as to displacement by movement of the modulator in said modulator chamber, the modulator dividing the modulator chamber into pressure chambers, means on the modulator exposed to the respective pressure chambers, said casing having low pressure intake and high pressure outlet passages operatively communicating with said pump chamber, means defining fluid pressure passageways from the high pressure passage to said modulator controlling pressure chambers, a plunger-type control valve in control of said passageways, means normally biasing said control valve into a position to control high pressure fluid movement through the passageway which communicates with the pressure chamber that will effect maximum pump displacement position of the modulator in'said modulator chamber, means for effecting communication between said high pressure passage and a pressure responsive area of the valve to shift the valve in opposition to said biasing means for modifying movement of pressure fluid to flow through the passageway that communicates with the remaining pressure chamber to adjust the modulator to reduce fluid displacement by the pumping means, a piston extension from the pressure responsive area of the plunger valve, and means for selectively subjecting said piston extension to fluid pressure from said high pressure passage.

3. In a variable displacement pump, a casing definingoneness iaamjodulator chamber, .amodulatormovable inisaidchamv ber and;providingia pump chamber, fluid pumping means operable in said pump chamber and adjustable as to displacement by movement of the modulator-in sai'd modulator chamber, ,the'modulator dividing the'modulator chamber intoupressurezchambers, meanson the modulator exposed to the respective pressure chambers, said casing having,low;p1tessure intake and high'pressure outlet passages'operatively communicating with said pump chamber, means definingfiuidpressure passageways from the high pressure 'passage to said modulator controlling pressurechambers, a plunger-type control valve in control 'ofssaid passageways, means vnormally biasing said control valve ;into a. position to control high pressure fluid movement through the passageway which communicates withthe pressure chamber that will effect maximum pump vdisplacementposition of'the modulator in said. modulator chamber,-meansfor effecting communication between said high pressure passage and a pressure responsive area of the valve to shift the valve in opposition to said biasing means for modifying movement of pressure fluid to flow through the passageway that communicates with the remaining-pressure chamber to adjust the modulator to reduce fluid displacement by the pumping means, a piston extension from thepressure responsive area of the plunger valve, andvalve control meanslfor selectively subjecting said;pistonI-extension-to'fluid pressure from said high pressure passage-or to atmosphere.

4. -In a variable displacement pump, a casing defining a modulator chamber, a modulator movable in said chamber and providing a pump chamber, fluid pumping means Operable in said pump chamber and adjustable as to displacement by movement of the modulator in said modulator chamber, the modulator dividingthe modulator chamher into pressure chambers, means on the modulator exposed to the respective pressure chambers, said casing having low pressure intake and high pressure outlet passages operatively communicating with said pump chamber, :means definingfluid pressure passageways from the high ,pressurepassage to said modulator controllingpressure chambers, a-plunger-type control valve .in control of said passageways, means normally biasing said control valve into aposition to control high pressure fluid movement through the passageway which communicates with the pressure chamber that will effect maximum pump displacement position of the modulator in said modulator chamber, means for effecting communication between said high pressure passage and the portion of the plunger valve opposite to said biasing means providing a shoulder against whichhighpressurefluid is operative to shift the valve in opposition to said biasing means forwmodifying movement of the pressure fluid to flow through the peesageway that communicates with the remaining pressure chamber foradjusting the modulator to reduce fluid displacement by the pumping means, an integral piston extending-from said shoulder and reducing the effective pressure responsive area of the shoulder, andmeans for selectively exposing said piston to the effect of pressure fluid iirom said high pressure passage to act supplemental to the pressure fluid acting on said shoulder.

, ,5. Ina variable displacement pump, a casing defining amodulatorchamber, a modulator movable in said chamher and providingapump chamber, fluid pumping means operable insaid pump chamber and adjustable as to displacement by movement of the modulator in said modulator chamber, the modulator dividing the modulator chamher into pressure chambers, means on the modulator exposed to the respective pressure chambers, said casing having low pressure intake and high pressure outlet passages operatively communicating with said pump chamber, means defining fluid pressure passageways from the high pressure passage tosaid modulatorcontrolling pressure chambers, a plunger-type control valve in control of said passageways, means normally biasing said control valve into a position to control high pressure fluid movement through :the passageway which communicates with the pressure chamber that will effect maximum pump dis placement position of the modulator 'in isaidmodu'lator chamber, means 'fol' eifecting communication between said high 'pressurerpassage and=the portion of'the pIunger'valve opposite to :said biasing means providing a' shoulder against which high pressure fluidiis operative'tozshift the valve in-opposition to said biasing means for'modifying movement of the pressure fluid Ito flow through the =passageway that communicates with the remaining pressure chamber for adjustingthe modulator to reduce fiuid displacement by the pumping means, anintegralpiston ex tending from said shoulder and being of substantially smaller diameter than the valve plunger, said casing :providing a bore forslidable reciprocationlherein.of said pis-' ton, and means providing apassage from saidhigh pressure passage to said bore and having'a valve'therein for controlling movement of high :pressure fluid selectively into said borefor supplementing pressure of the, pressure fluidion said shoulder.

6. In a variable displacement pump, a casing defining a modulator chamber, a, modulator movablein said chamber and providing a pump chamber, fluid pumping means operable in said pump chamber and adjustable as to displacement by movement of the modulator in said modulator chamber, the modulator dividing the modulator chamber into pressure chambers, means on the modulator exposed to the respective pressure chambers, said casing having low pressure intake and high pressure outlet passagesoperativelycommunicating with said pump chamber, means defining fluid pressurepassageways from thehigh pressure passage. to said modulator controlling pressure chambers, a piunger-type control valve in control of said passageways, means normally biasing said control valve into a position to control high pressure fluid movement through the passageway which communicates with the pressure chamber that will effect maximum pump displacement position of the modulator .in said modulator chamber, means for effecting communication betweensaid high pressure passage and the portion of the plunger valve opposite to said biasing means providing a shoulder against which .high pressure fluid is operative to shift the valve in opposition to said biasing means for modifying movement of the pressure fluid to flow through the passageway that communicates with the remaining-pressure chamber for adjusting the modulator to reduce fluid displacement by the pumping means, an integral piston extending from said shoulder and reducing the effective pressure responsive area of the shoulder, and means for selectively exposing said piston to the effect of pressure z'fluid from said high pressure passage to act supplemental'to the pressure fluid acting on said shoulder, saidpiston including a plurality of pressure responsive areas successively subjectable to the pressure fluid.

7. In a variable displacement pump, a casing deflni'ng a modulator chamber, a modulator movable in saidchamber and providing a pump chamber, fluidipumping means operable in said pump chamber and adjustable as to displacement by movement of the modulator in said modulator chamber, the modulator dividing the modulator chamber into pressure chambers, means on the modulator exposed to the respective pressure chambers, saidrcasing having low pressure intake and high pressure outletipassages operatively communicating with said "pump chamber, means defining fluid pressure passageways from the high pressure passage to said modulator controlling pressure chambers, a plunger-type control valve in control of said passageways, means normally biasing said control valve into a position to control high pressure fluid movement through the passageway which communicates with the pressure chamber that will effect maximumpump displacement position of the modulator insaidmodulat'or chamber, one end portion of the control valve plunger having a pair of spaced pressure fluid receptive shoulders respectively fluid pressure isolated from one :a'noth'ergan'd means for effecting communication between said shoulders and said high pressure passage and said shoulders to impose high pressure fluid thereon in the operation of the pump to move the valve in opposition to said biasing means for modifying movement of high pressure fluid to fiow through the passageway that communicates with the remaining pressure chamber to adjust the modulator to reduce fluid displacement by the pumping means, and means for selectively excluding one of said shoulders from the effects of pressure fluid.

8. In a variable displacement pump, a casing defining a modulator chamber, a modulator movable in said chamber and providing a pump chamber, fluid pumping means operable in said pump chamber and adjustable as to displacement by movement of the modulator in said modulator chamber, the modulator dividing the modulator chamber into pressure chambers, means on the modulator exposed to the respective pressure chambers, said casing having low pressure intake and high pressure outlet passages operatively communicating with said pump chamber, means defining fluid pressure passageways from the high pressure passage to said modulator controlling pressure chambers, a plunger-type control valve in control of said passageways, means normally biasing said control valve into a position to control high pressure fluid movement through the passageway which communicates with the pressure chamber that will effect maximum pump displacement position of the modulator in said modulator chamber, one end portion of the control valve plunger having a pair of spaced pressure fluid receptive shoulders respectively fluid pressure isolated from one another, and means for effecting communication between said shoulders and said high pressure passage and said shoulders to impose high pressure fluid thereon in the operation of the pump to move the valve in opposition to said biasing means for modifying movement of high pressure fluid to flow through the passageway that communicates with the remaining pressure chamber to adjust the modulator to reduce fluid displacement by the pumping means, and

means for selectively excluding one of said shoulders from the effects of pressure fluid, said last mentioned means being operable when excluding said one shoulder from the effects of pressure fluid to expose said one shoulder to atmosphere.

9. In a variable displacement pump construction, a housing member providing a modulator chamber opening therein and having opposite faces directed axially relative to the modulator chamber opening, a pair of easing plates respectively engaging said iiices and cooperating with said housing member to at least partially enclose said moduiator chamber, a modulator member slidably adjusiably movable within said modulator chamber and dividing the modulator chamber into opposite sub-chambers, said modulator providing a pump chamber, fluid displacement pumping means operable in said pump chamber, one of said plates, having low pressure and high pressure ports opening into said pump chamber in fluid displacement relation to said pumping means, said one plate having a plunger valve bore therein, a plunger valve reciprocably operable in said bore, passages in said one facing plate and said housing member communicating with said plunger bore and with said sub-chambers, said plunger valve bore being in direct communication with both of said ports, said plunger valve being operable for controlling communication between said ports through said passages with said sub-chambers, one of said passages comprising a groove in said one plate, and means closing said groove.

References Cited in the file of this patent UNITED STATES PATENTS 334,079 Mason Ian. 12, 1886 344,501 Schutte June 29 1886 559,379 Green May 5, 1896 1,943,929 Rayburn Jan. 16, 1934 2,031,749 Vincent Feb. 25, 1936 2,062,310 Hittell Dec. 1, 1936 2,080,810 Douglas May 18, 1937 2,142,275 Lane Jan. 3, 1939 2,214,817 Harrington Sept. 17, 1940 2,238,062 Kendrick Apr. 15, 1941 2,238,063 Kendrick Apr. 15, 1941 2,291,424 Wichorek July 28, 1942 2,296,876 Samiran et al Sept. 29, 1942 2,420,155 1 Tucker May 6, 1947 2,564,237 Segsworth Aug. 14, 1951 2,606,503 Shaw Aug. 12, 1952 FOREIGN PATENTS 154,632 Great Britain Dec. 9, 1920 528,950 Great Britain Nov. 11, 1940 574,359 Great Britain Jan. 2, 1946 

